1. Field of the Invention:
This invention relates to a driving circuit for a liquid crystal display panel, and more particularly to an improvement of the driving circuit for equivalently reducing picture defects.
2. Description of the Prior Art:
Matrix type large area displays have been developed as means for displaying graphs, characters and images. Among various kinds of such displays, liquid crystal display panels have considerable potential. A typical structure is shown in "Applied Physics" No. 24 (1981) pp. 357 to 362, A. J. Snell, et al. "Application of Amorphous Silicon Field Effect Transistors in Addressable Liquid Crystal Display Panels" and has a glass substrate on which a plurality of thin film MOS field effect transistors (hereinafter, referred to as a TFT) as switching elements are mounted in a matrix form which is covered with a transparent cover plate with liquid crystal inserted between the glass substrate and the transparent cover plate. The inner surface of the cover plate is coated with a transparent conducting layer of Indium Tin Oxide (ITO). The transmittance of the liquid crystal to respective picture elements is controlled by selectively driving the TFT's. The TFT's are formed in a polycrystalline silicon layer or an amorphous silicon layer. By use of the TFT's, the resolution rises to the extent practical, but the density of picture defects is not reduced. It is impossible by present production techniques to increase the yield of TFT's up to one. The picture elements corresponding to the defective TFT's appear as picture defects. If the yield of the TFT's is assumed as 99.9%, 250 picture defects appear on a display panel having picture elements in a matrix of 500 rows and 500 columns. Such a defective image cannot be practically used in a market. Further, the high density of picture defects limits the application of the liquid crystal display panels to small size displays.